Bone grafts are second only to blood transfusions on the list of transplanted materials worldwide. In addition, the estimated worldwide market for bone graft material is about £650 million each year. Every year, up to 4 million bone replacement procedures are performed worldwide which require the use of a bone graft or scaffold. The most common clinical treatment is an autograft whereby bone is taken from the patient's own body and reimplanted. However there is a limited amount of bone which can be removed from a particular donor site and additional invasive surgery is required for reimplantation. Another option is the use of an allograft whereby bone is removed from an organ donor. Problems with this approach stem from the origin of the bone from a separate donor. A higher risk of infectious disease transmission is associated with such material. In addition, fewer growth factors are present in such donor bone because it contains no living cells. These growth factors aid the growth of new bone. An ideal implantable scaffold that would promote bone formation while facilitating load bearing would reduce the need for allografts or autografts. However, presently these traditional approaches constitute over 90% of all bone graft procedures. The reason for this shortfall, despite the problems described above, is that a vascularised, mechanically competent, osteoconductive scaffold that could be used to produce bone in vitro or cause complete osteogenesis in vivo remains to be developed. Such a product would have significant commercial potential.
Various attempts have been made using numerous synthetic materials to produce viable scaffolds for bone grafting. Examples include polystyrene, titanium, polyllactic acid (PLLA), polyglycolic acid (PGA) and polylacticcoglycolic acid (PLGA). However, all these materials have associated problems and drawbacks including the risk of infection and difficulties allowing adequate resorption to promote vascularisation and ingrowth of new bone. Biological materials such as collagen, gelatin, chitosan, agarose and glycosaminoglycan (GAG) based substrates have also been used. However these materials do not have mechanical properties sufficient to allow load bearing after implantation.